On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks

02/11/2020
by   Ludovic Thomas, et al.
0

Flow reshaping is used in time-sensitive networks (as in the context of IEEE TSN and IETF Detnet) in order to reduce burstiness inside the network and to support the computation of guaranteed latency bounds. This is performed using per-flow regulators (such as the Token Bucket Filter) or interleaved regulators (as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are beneficial as they cancel the increase of burstiness due to multiplexing inside the network. It was demonstrated, by using network calculus, that they do not increase the worst-case latency. However, the properties of regulators were established assuming that time is perfect in all network nodes. In reality, nodes use local, imperfect clocks. Time-sensitive networks exist in two flavours: (1) in non-synchronized networks, local clocks run independently at every node and their deviations are not controlled and (2) in synchronized networks, the deviations of local clocks are kept within very small bounds using for example a synchronization protocol (such as PTP) or a satellite based geo-positioning system (such as GPS). We revisit the properties of regulators in both cases. In non-synchronized networks, we show that ignoring the timing inaccuracies can lead to network instability due to unbounded delay in per-flow or interleaved regulators. We propose and analyze two methods (rate and burst cascade, and asynchronous dual arrival-curve method) for avoiding this problem. In synchronized networks, we show that there is no instability with per-flow regulators but, surprisingly, interleaved regulators can lead to instability. To establish these results, we develop a new framework that captures industrial requirements on clocks in both non-synchronized and synchronized networks, and we develop a toolbox that extends network calculus to account for clock imperfections.

READ FULL TEXT
research
05/29/2023

Network-Calculus Service Curves of the Interleaved Regulator

The interleaved regulator (implemented by IEEE TSN Asynchronous Traffic ...
research
08/07/2020

On Packet Reordering in Time-Sensitive Networks

Time-sensitive networks (IEEE TSN or IETF DetNet) may tolerate some pack...
research
09/06/2021

Analysis of Dampers in Time-Sensitive Networks with Non-ideal Clocks

Dampers are devices that reduce delay jitter in the context of time-sens...
research
10/12/2021

Worst-case Delay Bounds in Time-Sensitive Networks with Packet Replication and Elimination

Packet replication and elimination functions are used by time-sensitive ...
research
07/11/2021

Some Properties of Length Rate Quotient Shapers

Length Rate Quotient (LRQ) is the first algorithm of interleaved shaping...
research
06/04/2018

Nanoseconds Timing System Based on IEEE 1588 FPGA Implementation

Clock synchronization procedures are mandatory in most physical experime...
research
08/24/2022

Worst-case Delay Analysis of Time-Sensitive Networks with Deficit Round-Robin

In feed-forward time-sensitive networks with Deficit Round-Robin (DRR), ...

Please sign up or login with your details

Forgot password? Click here to reset